Search

High-power piezoelectric characteristics under continuous driving were studied on some bismuth layer-structured ferroelectric ceramics, i.e., Sr0.25Bi2.75Ti0.75Ta1.25O9 (SBTT, m = 2), Bi4Ti2.98V0.02O12 (BITV, m = 3), Bi4Ti3O12–SrBi4Ti4O15 + MnCO3 0.2 wt % (BIT–SBTi, m = 3, 4), and (Sr0.7Ca0.3)2Bi4Ti5O18 + MnCO3 0.2 wt % (SCBT, m = 5). The vibration velocities, v 0–p, of SBTT, BIT–SBTi, and SCBT ceramics were above 2.0 m/s at 5 V/mm. Also, we observed that the resonance frequency changes and temperatures on the sample surfaces for SBTT, BIT–SBTi, and SCBT ceramics were less than 1.0% and 50 °C at a v 0–p of 2.0 m/s, respectively. The high-power characteristics of the ceramics were superior to those of BITV and hard Pb(Zr,Ti)O3 (abbreviated as PZT) at a vibration velocity v 0–p > 0.6 m/s. Therefore, SBTT, BIT–SBTi and SCBT ceramics are promising candidates for lead-free high-power applications requiring high vibration velocity and frequency stability.

A resonant-type ultrasonic tracer is developed and the relationship between the resonance frequency and the diameter of hollow magnetic microspheres is clarified experimentally. Flow visualization of a water/solid microparticle suspension characterized by Rayleigh scattering is demonstrated using the tracer.

Ge islands are grown by molecular beam epitaxy (MBE) on Si(111) surfaces with an SPE-grown buffer layer, which was expected to prevent intermixing between the epitaxial Ge layer and the Si substrate. The epilayer composition analyzed from the spacing of the Moiré fringe indicates that the Ge islands should be a Si-Ge alloy rather than pure Ge and that the alloying of Ge with Si is greater near the edges of the island. The alloying phenomenon was verified by the compositional depth profile analysis using the scanning Auger electron microscope (SAM) technique. The Si incorporation into the Ge islands observed here cannot be explained by a bulk diffusion mechanism and is a seriously anomalous phenomenon since Si diffusion into Ge would be negligible at the growth temperature and time used ill this experiment.

Heat flux to the material surfaces in the scrape-off layer of a tokamak plasma is investigated experimentally. The time response of heat flux measurement has been improved to 0.2 ms by the recently developed thin-film thermometer. The result shows that the heat flux is calculated from a simple sheath model including secondary electron emission effects even if epithermal electrons are present.

TEM observation of the segregated microstructure in sputtered Co–Cr films was conducted. The specific segregated microstructure was observed in the film composition range of 15.3–24.3 at%Cr–Co. The results present a new model for the origin of the segregation where two-phase separation into magnetic and non-magnetic phases occurs in a single hcp phase. The ferromagnetic Co-rich regions in a crystallite are supposed to be embedded in nonmagnetic Cr-rich matrix, with a wall-like figure perpendicular to the substrate plane.

Observation is made of a cross section including the growth direction of an MBE grown GaAs–Al0.28Ga0.72As superlattice structure by a transmission electron microscope with a resolution of 1.4 Å. Relevant atoms are observed to be regularly aligned even across the heterointerface. There is no alloy clustering observed in the ternary alloy layer. Dislocation is clearly observed as a local disorder in lattice alignment for the first time in the MBE grown layer.

A TiC coated Mo material has been tested as a limiter in the JFT-2 tokamak. The surface temperature of the limiter is measured with an infrared scanning camera. The maximum surface temperature rise during a steady state discharge with a neutral beam power of 700 kW is around 230°C in 25 msec and the heat flux density to the limiter is 1–4 kW/cm2. The maximum temperature rise during a current disruption with the beam power of 1 MW is about 100°C in 100–600 µsec and the density is the order of 50 kW/cm2. The TiC coated Mo material can be proof against such a high load.

Misfit dislocation structures introduced at Si1-x Ge x /Si (001) Interfaces were studied using transmission electron microscopy to understand the relaxation mechanism of lattice misfit in this material system. Misfit dislocations observed at the interfaces for x≤0.5 are inclined 60° dislocations introduced by glide processes. The density of the misfit dislocations increases with mole fraction or thickness of the Si1-x Ge x as a result of the Hagen-Strunk multiplication mechanism. The threading dislocations contained in the epilayers originate in transition dislocation segments appearing during the multiplication processes. In contrast with these results, the misfit dislocations observed at the Ge/Si interface are the 90° -type introduced by climb processes. The misfit dislocations were regularly distributed with an average spacing of ∼100Å, which is sufficient to relax the 4.2% misfit. Thus, the relaxation mechanism of the misfit strain in the Si1-x Ge x /Si system changes depending on the lattice misfit.

Observation au microscopie electronique de haute resolution de particules ultrafines de dimension inferieure a 6 nm formes par coprecipitation

The threading dislocation density in Ge layers grown by molecular beam epitaxy on Si substrates can be reduced by insitu thermal annealing during deposition. The Ge/Si interfaces of nonannealed and insitu annealed samples are observed by plan-view transmission electron microscopy to understand the dislocation-reduction mechanism. The results suggest the following: (1) the formation of dislocation networks and half-loops terminating at the interfacial misfit dislocation array is enhanced by the thermally induced strain of insitu annealing; (2) the dominant mechanism of dislocation reduction is the shrinkage of dislocation networks and half-loops into the interface; (3) dislocation line tension is the driving force of this shrinkage.